Method for producing a hot worked body

ABSTRACT

A METHOD FOR PRODUCING A HOT WORKED BODY HAVING A LOW INCIDENCE OF OXIDE INCLUSIONNS. IT COMPRISES THE STEPS OF CONSOLIDATING POWDER COMPRISED OF METALLIC PARTICLES INTO A POROUS BODY, SUBSTANTIALLY SEALING THE SURFACE OF SAID BODY BY CLOSING SURFACE PORES, HEATING SAID BODY, AND HOT WORKING SAID BODY.

United States Patent 3,740,215 METHOD FOR PRODI(J)(lI)Il;1G A HOT WORKED B David L. Burk, Pittsburgh, and Orville W. Reen, Lower 3,740,215 Patented June 19, 1973 clusions. It comprises the steps of consolidating powder comprised of metallic particles into a porous body, substantially sealing the surface of said body by closing surface pores, heating said body and hot working said body.

5 The step of sealing the surface was found to substantially i g l g gi %g? to Allegheny Ludlum Industries preclude internal oxidation during both heating and hot N0 'Drawiug. I iled Aug. 24, 1970, Ser. No. 66,641 o king. It provides a dense surface on the body which Int. CL zz 7/00 will resist the penetration of harmful gases at elevated U,s CL 75 20g 7 Claims temperatures. In addition, it is advantageous as it rapidly 10 provides a dense surface which is of the same material as the interior, and thus allows the body to be handled in ABSTRACT OF THE DISCLOSURE the same manner as a solid bar.

A method for producing a hot worked body having a Self-sealing has been disclosed in the past for various low incidence of oxide inclusions. It comprises the steps reasons, e.g., to improve mechanical strength or to give of consolidating powder comprised of metallic particles direction to gas flo Within a Y- into a porous body, substantially sealing the surface of 709, 3,183,086, and 3,231,430, which respectively issued said body by closing surface pores, heating said body, and on Nov. 6, 1956, May 11, 1965, and Jan. 25, 1966, dishot working said body. close self-sealing. None of these patents, however, disclose or suggest that self-sealing would prevent internal oxidation of a body which is heated and subsequently The present invention relates to a method of producing stretched during hot working a hot Worked y having a low incidence of Oxide It is accordingly an object of this invention to provide a clusions and more Particularly t0 9 method of Producing method for producing a hot worked body having a low a hot Worked y having a 10W lhcldenoe of oxide incidence of oxide inclusions from powder comprised of clusions from powder comprised of metallic particles. t lli i l y materials are Stronger, last lollgel', cost less, The method of the present invention comprises the steps and are more easily designed and fabricated than the bflst of consolidating powder comprised of metallic particles materials available y a few years y can now be into a porous body, substantially sealing the surface of fashioned into Smaller Parts, large! p and more said body by closing surface pores, heating said body, P Shapes than ever before- Largely responsible and hot working said body. Consolidating can involve a creating this advancement in materials technology are cold pressing, hot pressing, or intering operation 01- a modern powder metallurgy processes. combination of cold pressing and sintering or hot pressing P er metallurgy Processes frequently involve hot and sintering. Sintering should be performed in a non- Working as a means o bringing Consolidated metallic oxidizing atmosphere, e.g., a vacuum, inert gas or reducbodies to near one hundred percent of r ported W ug ing gas. Sealing can involve fusion of the surface to fill y- H0t Working and heating hot Working must, the pores or mechanical treatment to collapse the pores. however, he Perl-01111:d in a HOH-OXidiZhJg atmosphere to Illustrative means of fusing the surface are induction preclude internal oxidation of the bodies, as internal oxiheating, plasma torch fusion, and electron bombarddation Will limit the attainable density and deleteriously ment, Illustrative methods of mechanically sealing the affect properties. Consolidated metallic bodies are parsurface are burnishing, machining, and peening. Burnishticularly susceptible to internal oxidation during hot working is the preferred sealing treatment as it is applicable ing as they have an interconnected porosity which acover a wide range of particle properties and initial densicelerates oxygen diffusion. ties. Hot working can involve any of the known methods Various methods have been attempted to preclude inwhich include extrusion, rolling, swaging, drawing, and ternal oxidation during hot working and heating for hot forging. It can be performed in air or other oxygen conworking. One method involved canning of a consolidated t aining atmospheres. powder body under vacuum and hot working of the The powder which is to form the hot worked composite canned assembly. This process provided adequate proteccan be chosen from a Wide spectrum of metals, mixtures tion from oxidation but added extra costs to the hot workof metals, and mixtures of metals and non-metals. Illusing operation as it requires a great deal of work in pretrative metals are stainless steel, tool steel, copper, and paring the can and subsequently removing it. A canning bronze. Illustrative mixtures are copper-carbon and procedure is disclosed in US. Pat. No. 2,932,882 which graphite-bronze. issued on Apr. 19, 1960. A second method involved The following examples are illustrative of the invention. heating in a non-oxidizing atmosphere. This process was Predetermined amount of mesh powder from two disadvantageous insofar as internal oxidation would 55 atomized heats (A +B) were blended to produce a comoccur, unless special precautions were taken when the position which, after sintering, fell within the chemical body was transferred from the heating furnace to the hot specification of A151. Type 304 stainless steel. The blend working apparatus. Another method involved impregnaratio and chemical composition of the constituent heats tion of the body with a hydrocarbon compound which are listed below in Table I.

TABLE I Percentage Composition of heat of heat in Heat blend 0 Mn P 5 Si Cr Ni Fe A 26.0 0.44 0.29 0.018 0.010 2.06 18.19 12.37 Bal. B 74.0 0.009 0.18 0.003 0.006 1. 7s 17. 92 12.40 Bal.

evolves a protective vapor during heating. This process Three bodies were prepared from the blend. Loose is not totally satisfactory as it employs a material diiterent powder was poured, tamped, and vibrated into rubber from the metal of the body. It is disclosed in US. Pat. isostatic consolidating bags measuring approximately 3.2

No. 3,152,893 which issued on Oct. 13, 1964.

The present invention provides a method for producing a hot worked body having a low incidence of oxide ininches in diameter by 9 inches long, hydrostatically consolidated at pressures of 20, 25, and 30,000 p.s.i. and vacuum sintered for six hours at 2400 F. The bodies were about 2.75 inches in diameter and about 7 inches long.

The bodies were prepared for extrusion by drilling a inch hole through their centers and by machining the outer diameters to 2.62 inches. Both the inner and outer diameters as well as the ends and corners were then burnished. The burnished outer diameter was 2.60 inches. Extrusion was subsequently carried out with the bodies at a temperature of from 2000 to 2200 F. The bodies were heated in air with an induction heating coil.

The extruded bodies were examined metallographically for the presence of internal oxidation. The examination revealed that internal oxidation was not present. Burnishing provided a dense surface on the bodies which resisted the penetration of harmful gases during heating and hot working and, thereby, precluded internal oxidation.

From the above paragraphs it will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific examples thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they should not be limited to the specific examples described herein.

We claim:

1. A method of producing a hot worked body having a low incidence of oxide inclusions from powder comprised of metallic particles, which comprises the steps of: consolidating powder comprised of metallic particles into a porous body; substantially sealing the surface of said body by closing surface pores; heating said body in an oxidizing atmosphere; and hot working said body in an oxidizing atmosphere, said sealing of said surface substantially precluding internal oxidation during said heating and said hot working by providing a dense surface which resists the penetration of harmful gas at elevated temperatures.

2. A method according to claim 1 wherein the surface is substantially sealed by fusing the surface to fill the pores.

3. A method according to claim 1 wherein the surface is substantially sealed by mechanically treating the surface to collapse the pores.

4. A method according to claim 3 wherein said surface is mechanically treated by burnishing said surface.

5. A method according to claim 1 wherein said powder is consolidated by cold pressing powder and sintering said pressed powder in a non-oxidizing atmosphere and wherein said body is hot worked by extruding said body.

6. A method according to claim 1 wherein said body is heated in air.

7. A method according to claim 1 wherein said metallic particles are steel particles.

References Cited UNITED STATES PATENTS 2,215,723 9/1940 Jones -208 R 2,220,641 11/1940 Davis 75200' X 2,839,397 6/1958 Cavanaugh 75222 2,997,777 8/1961 Davies 29-182 3,183,086 5/1965 Kurtz et a1 75208 R CARL D. QUARFORTH, Primary Examiner R. E. SCHAFER, Assistant Examiner US. Cl. X.R. 

